1. Field of the Invention
The present invention relates to temperature sensors. More specifically, the present invention is directed to a temperature sensor utilized as a heat conductivity detector in a detector cell for fluid analysis.
2. Description of the Prior Art
The use of detector cells for determining the conductivity of a fluid passed therethrough is well-known in the art as shown in U.S. Pat. No. 3,243,991. Such cells use an electrically heated element in the form of a thermistor bead arranged within the cell and exposed to the fluid flow whereby the electrical resistance of the thermistor bead changes with the thermal conductivity of the fluid since the heated element loses heat more rapidly to fluids with a high heat conductivity. In most applications the heat conductivity detector cells are provided in pairs with one of the cells being arranged to have the fluid to be analyzed flowing therethrough while the other cell is provided with a comparison or reference fluid flow. The detector cells have been used to measure the concentration of specific components in a fluid and to detect the fluid components successively appearing at the outlet of a separating column of a chromatograph. In such an application, one cell would be provided with the output from a column which output would include the unknown gas and a carrier gas while the other cell would be provided with only a carrier gas flow. Such prior art thermistors and detector cells have several inherent disadvantages. Specifically, the thermistor beads have considerable mass whereby a rapid change in the heat conductivity affect of the different fluids is not reflected by a rapid change in the thermistor characteristics. Since such thermistor beads are often arranged on thin connecting or suspension wires, the structure is sensitive to vibration which causes electrical noise in the output signal. Such a thermistor bead and hanging wire structure is also very fragile, and, the deliberate reproducibility of substantially identical thermistors is virtually impossible. Accordingly, matched pairs of prior art bead thermistors are selected from hundreds of thermistor sensors by expensive electronic matching. The production of such thermistor sensors is also not suited for mass production whereby the cost of the thermistor devices is relatively expensive. Accordingly, it would be desirable to provide a solid state thermistor using solid state technology to enable the mass production of such thermistor devices with extreme uniformity thereof.